1. Field of the Invention
The present invention relates to a process for producing a nickel compound containing lithium and a high capacity nonaqueous electrolytic battery using the nickel compound containing lithium as a positive active material.
2. Description of the Related Art
With the recent development of portable electronic apparatus, it has been desired to develop high performance batteries. A lithium ion battery comprising a carbon material as a negative electrode and lithium cobaltate in the form of lamination composite oxide as a positive electrode has been put into practical use as a nonaqueous electrolytic battery having a high operating voltage and a high energy density. However, since lithium cobaltate is scarce and expensive, lithium-containing manganese composite oxides or lithium nickelate has been proposed as a substitute. These composite oxides are positive active materials for so-called secondary 4 V lithium battery having an average operating voltage of about 4 V.
On the other hand, since the development of interated circuits which operate at a voltage as low as 3 V or lower is under way, or from the standpoint of the safety of battery, it can be presumed that the demand for secondary 3 V nonaqueous electrolytic battery will be growing in the future. However, as positive active materials for secondary 3 V nonaqueous electrolytic battery there have been known only LiMnO.sub.2 and V.sub.2 O.sub.5. Even these materials are much disadvantageous in discharge capacity and cycle life and thus are extremely limited to memory back up in their use.
Further, it has been recently reported that nickel oxyhydroxide can be used as an positive active material for secondary 3 V nonaqueous electrolytic battery (64th Convention of The Electrochemical Society of Japan; Lecture No. 3A06). This report says that nickel oxyhydroxide exhibits an initial discharge capacity as high as 285 mAh/g, which corresponds to a percent utilization of not less than 95%, with its theoretical discharge being about 290 mAh/g. Thus, nickel oxyhydroxide can be fully used for purposes requiring a high energy density battery such as power supply for notebook personal computer. However, since nickel oxyhydroxide is a positive active material in charged state, it cannot be directly combined with an active negative electrode material in discharged state such as graphite to prepare a battery.
Accordingly, either the use of an active negative electrode material in charged state such as graphite having lithium occluded therein, metallic lithium and lithium alloy or the producing of an positive active material in discharged state is essential. From the standpoint of the safety and stability of the active material during the production of battery, the latter approach is preferred. In other words, the use of a nickel compound containing lithium produced by discharging nickel oxyhydroxide as an positive active material and an active material in discharged state such as graphite as an active negative electrode material makes it easier to prepare a battery. Since the positive active material is in discharged state and thus is highly stable to oxygen or water content, the necessity of controlling the exposing atmosphere can be lessened, making it possible to simplify the production facilities and hence add to the advantage in cost.
At present, however, the nickel compound containing lithium as a discharge product of nickel oxyhydroxide can be produced only by the electrochemical reduction of nickel oxyhydroxide in an organic electrolytic solution containing a lithium salt. Accordingly, the application of the foregoing process for producing battery to such a nickel compound containing lithium requires the employment of steps of At previously preparing an electrode comprising nickel oxyhydroxide as an active material, subjecting the nickel oxyhydroxide to an electrochemical process to produce a nickel compound containing lithium as a discharge product, and then washing the material to remove the electrolytic solution therefrom and drying the material. These steps are very difficult to carry out and are disadvantageous in productivity, cost and quality. It has thus been desired to establish a simple and effective process for the synthesis of such a nickel compound containing lithium.
As previously mentioned, nickel oxyhydroxide has been expected to be a most suitable positive active material for secondary 3 V nonaqueous electrolytic battery. However, since nickel oxyhydroxide is in charged state itself, it is necessary that a nickel compound containing lithium in discharged state be used as the positive active material to be combined with graphite or the like as an active negative electrode material in discharged state to prepare a battery. However, no simple and effective process for the synthesis of such a nickel compound containing lithium has been found. It has thus been desired to establish such a synthesis process.